HR: 0800h
AN: H31B-0352    [Abstracts]
TI: Combined Radar and Radiometer Analysis of Precipitation Over Land
AU: * Hammerschmidt, B
EM: bhammer@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523- 1371, United States
AU: Kummerow, C
EM: kummerow@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523- 1371, United States
AB: Passive microwave imagers have long been used to detect rainfall over the world's oceans. Over land, passive microwave imagers have historically relied on the use of high frequencies (i.e., 85 GHz) to detect ice scattering signals and relate this scattering signal to a surface rainfall. Errors with this retrieval are caused by inexact retrievals of the ice water paths, the relationship between ice water path and surface rainfall and by the parallax effect - a geometric displacement between the ice scattering and surface rainfall introduced by the viewing geometry of microwave sensor. This study analyzed precipitation over the southeast United States in the summer months of 1998 to 2000, using the TRMM Microwave Imager (TMI) and Precipitation (PR) on board the Tropical Rainfall Measuring Mission (TRMM). Correlations between 85-GHz brightness temperatures (Tb) and PR-derived surface rainfall, without accounting for the parallax effect, ranged from -0.16 to -0.47 for individual months. By accounting for the parallax effect and retrieving a surface rain rate directly below the ice layer that is being observed, the correlations with Tb 85 improved slightly to the -0.23 to -0.52 range. Further analysis of the ice scattering signal showed that stratiform precipitation with moderate ice scattering had improved correlations with rainfall rate when observed 37-GHz Tbs were used instead of 85 GHz. Correlations between Tb37 and surface rainfall ranged from -0.36 to -0.71, while Tb 85 versus surface rainfall had correlations that ranged from -0.22 to - 0.47 in this rainfall category. This was a result of 37-GHz Tbs being influenced more directly by scattering and emission from the liquid layer. Correlation between the IWP, as derived from the TRMM radar, and the 85-GHz Tb depressions ranged from -0.47 to -0.72. This indicates that significant improvements in rainfall retrievals can still be achieved from either an improved understanding of the ice physics (needed to improve the above correlations) as well as improved understanding of the relationship between ice water aloft and surface rainfall in different meteorological regimes. To further explore the relation between radar derived IWP and radiometer signals, ice water paths were examined with a combination of both radar and radiometer observations. Specifically, different ice density and ice particle number concentrations were examined on the radar inferred ice water path. Stratiform precipitation showed good agreement with both radar and radiometer observations when relatively low density ice (e.g.. snow) particles were assumed. For convective pixels with significant ice scattering, significantly denser ice particles were generally required. Moreover, liquid water above the freezing level had to be added in over 50% of the profiles before a solution that was consistent with both radar and radiometer observations could be constructed. These results appear consistent with current cloud physics understanding.
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1855 Remote sensing (1640)
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting